1. Field of the Invention
The present invention relates to a remote access server and a communication system in which a dormant function is introduced, and to a resource management method for managing circuit resources that are provided in this remote access server.
2. Description of the Related Art
A remote access server (RAS) is used when a terminal device wishes to connect to the Internet by a dial-up connection. This RAS has the capability of connecting calls that are requested from a plurality of terminal devices by way of a circuit-switching network to an ISP (Internet Service Provider) server such as a Web server or mail server by way of the Internet.
When the terminal device in the above-described type of communication system is, for example, a portable telephone, the circuit to an RAS may sometimes be disrupted due to deterioration of the state of radio waves.
To remedy this type of problem, a communication system has been proposed in, for example, Japanese Patent Laid-Open Publication No. 2002-10341 that is provided with a dormant function for cutting the circuit connection with the data-link initiation reception side device (the above-described RAS) when a suspension of operation (hereinbelow referred to as a “dormant state”) occurs in the data-link initiation side device, i.e., the terminal device of an Internet user, and then reconnecting the circuit with the data-link initiation reception side device upon resumption of operation (active state) of the data-link initiation side device.
This dormant function is realized based on “MITF (Mobile Internet Access Forum) dial-up dormant protocol” (ARIB STD-T78 1.0, Jul. 27, 2001) which is the relevant standards of the PHS Internet Access Forum Standards (PIAFS) published by a corporate juridical person, the Association of Radio Industries and Businesses (ARIB) (HYPERLINK “http://www.arib.or.jp/”).
On the first page of these standards, the communication environment for realizing the dormant function is shown in FIG. 1.1 “Communication environment applying MITF dial-up dormant protocol” in “Positioning of MITF dial-up dormant protocol.”
In a communication system that employs this type of MITF dial-up dormant protocol, circuit resources that are provided in a RAS are distinguished between physical link resources, which are circuit resources for connecting to a terminal device by way of a circuit-switching network, and logical link resources, which are circuit resources for connecting to an ISP server by way of the Internet. When a particular call is set to the dormant state in an RAS, the physical link resource is released while the connection of the logical link resource of this call that is in the dormant state is maintained without change. Thus, even when the physical link resource is unexpectedly cut off due to such factors as the deterioration of the radio wave state in, for example, a portable telephone, the maintenance of the logical link resource allows the continuation of the original call by reconnecting only the physical link resource.
The above-described physical link resources are circuit resources such as a telephone lines, and there is consequently a limit to the number of physical link resources that can be provided in an RAS. As a result, the number of terminal devices that can connect to a circuit is limited by the number of physical link resources. With the rapid increase in Internet use in recent years, the connection capacity between an RAS and terminal devices has become inadequate, and there is the consequent problem that dial-up connection service cannot be provided for new calls from terminal devices and calls are lost.